Dehydration Process and Mechanism of Magnesium Nitrate Hexahydrate Using Thermal Analysis Technique
ZHONG Yuan1,2,3, WANG Min2,3, YUAN Junsheng1
1 School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130, China 2 Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China 3 Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, Xining 810008, China
Abstract: Magnesium nitrate-based molten salt has a wide application prospect as a medium temperature energy storage material forsolar thermal po-wer generation. The research on the dehydration process and mechanism of magnesium nitrate hexahydrate is of guiding significance for the preparation of magnesium nitrate. The dehydration process and mechanism of magnesium nitrate hexahydrate were studied in this work through simultaneously TG/DSC. The thermodynamic functions of dehydration reaction of magnesium nitrate hexahydrate were calculated. The dehydration products were characterized by XRD, Raman and DSC. The results of calculation show that magnesium nitrate hexahydrate is dehydrated to magnesium nitrate when the temperature is above 168.02 ℃ in standard state. In the process of program heating, first magnesium nitrate hexahydrate is melted to a solution, then magnesium nitrate dihydrate precipitates from the solution as the water loses. This dehydration process can be described according to the phase equilibrium of magnesium nitrate-water solution. Solid magnesium nitrate dihydrate is melted at 130 ℃. The melt is dehydrated to anhydrous magnesium nitrate, which involves a liquid-solid heterogeneous phase reaction. The melt is completely dehydrated to anhydrous magnesium nitrate at higher temperature than the calculated value, indicating that this dehydration reaction is thermodynamically spontaneous.
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2020, Vol. 34 
